The earlier patent applications respectively disclose several embodiments of an electromagnetically actuated locking hub assembly for part time four wheel drive vehicles and a locking differential assembly where one drive member of the differential is locked to another drive member of the differential for changing the mode of operation of the differential.
This patent application includes an axle disconnect assembly in addition to the power transmitting devices disclosed in the earlier patent applications.
Locking hub assemblies and axle disconnect assemblies are used in part time four wheel drive vehicles to disconnect the nondriven wheels in the two wheel drive mode to prevent back drive which causes unnecessary power consumption and wear.
The initial approach employed locking hub assemblies on the optionally driven wheels, normally the front wheels, that were manually disengaged to allow the optionally driven wheels to rotate independently of their drive axle. The major drawback of the locking hub is that the assemblies require the vehicle operator to lock or unlock each hub assembly manually to engage or disengage the optionally driven wheels from their drive axle. This approach is still used in some off road type four wheel drive vehicles but is generally regarded as unsatisfactory in highway type four wheel drive vehicles due to the requirement for manual operation.
A well known alternative to manually operated locking hub assemblies is an automatic locking hub assembly that engages automatically when power is applied to the front or optional drive axle in the four wheel drive mode.
An automatic locking hub assembly is disclosed in U.S. Pat. No. 4,192,411 granted to Mark J. Fogelberg Mar. 11, 1980 for an Automatic Locking Clutch and assigned to the Borg-Warner Corporation. This automatic locking hub assembly engages a drive axle and an associated wheel upon engagement of a four-wheel drive system, maintains engagement positively in the drive and coast modes of operation as well as during the transition between drive and coast, maintains engagement positively in the forward and reverse modes of operation as well as during the transition between forward and reverse and disengages automatically upon a slight direction reversal when the four-wheel drive system is disengaged. However, the automatic locking hub assembly uses a ring which develops high frictional drag to effect clutch engagement and which maintains this high frictional drag after clutch engagement even though it is not required to maintain clutch engagement.
The automatic locking hub assembly disclosed in U.S. Pat. No. 4,281,749 granted to Mark J. Fogelberg Aug. 4, 1981 for an Automatic Locking Clutch and assigned to the Borg-Warner Corporation incorporates several improvements including a wrapped spring to effect clutch engagement through a camming and load spring arrangement. The wrapped spring is tightened to develop the high frictional drag necessary for clutch engagement but then is loosened after clutch engagement to reduce frictional drag to a minimum. Use of the camming and load spring arrangement to effect clutch engagement also prevents gear clash and a prolonged blockage of clutch engagement which could be harmful to the wrapped spring.
Other alternatives have been employed to actuate a locking hub assembly such as by the use of a supplementary power source to actuate a locking hub assembly such as by the use of a supplementary power source to actuate a drive gear, or to employ pneumatic systems where vacuum or pressure motors or valves cause the drive gear to engage or disengage by spring pressure when the vacuum or fluid is removed, or to employ a solenoid for activating a drive gear into dynamic engagement.
For example, U.S. Pat. No. 4,694,943 granted to Harry A. Petrak Sep. 27, 1987 for a Ground Clutch Assembly discloses a ground clutch assembly in association with either an axle disconnect or a wheel hub that converts a vehicle from two-wheel drive to four-wheel drive and vice-versa by means of a camming assembly and a solenoid operated shift mechanism so that a moving vehicle can be converted without need to stop the vehicle, back up or change vehicle direction. The shift mechanism temporarily locks the camming assembly against rotation in advancing a drive gear into driving engagement with a receiving gear in converting to four-wheel drive. The camming assembly is also temporarily locked against rotation by the solenoid operated shift mechanism in disengaging the drive gear from the receiving gear in converting to two-wheel drive.
It will be appreciated that a solenoid operated locking hub assembly is more flexible in operation because the assembly responds to an electrical signal. Consequently the engagement and disengagement of the locking hub assembly can be controlled by the vehicle operator and/or activities of other power train components. However, the Petrak arrangement has a very complicated camming assembly that is operated by the solenoid for engaging or disengaging the locking hub assembly when the solenoid electromagnet is energized. Other drawbacks include lack of any provision for preventing gear clash when the drive gear is shifted into engagement with the receiving gear and use of a rotatable electromagnet for the solenoid that is energized by an onboard radio receiver and battery.
It is also known from U.S. Pat. No. 5,030,181 granted to Walter Keller Jul. 9, 1991 to provide a bevel gear differential that has a solenoid operated gear clutch for positively locking one of the side gears to the differential case. The solenoid operated gear clutch includes an armature plate that is attached to a sleeve that is slidably splined on the shaft of side gear and that has clutch teeth. When the electromagnet is energized, sleeve slides to the right as viewed in FIG. 1 of the patent drawing to engage the clutch teeth of the sleeve with cooperating clutch teeth on the case locking the side gear to the case. When the electromagnet is deenergized, the clutch is disengaged by a return spring. This arrangement requires a continuous energization of the electromagnet for clutch engagement. Another drawback of the arrangement is that it lacks any provision for preventing gear clash when the sleeve is shifted into engagement with the clutch teeth of the differential case.